Differentials
Acute bronchiolitis
SIGNS / SYMPTOMS
May cause cough and wheeze, and lead to shortness of breath, with or without asthma. In practice, acute viral bronchiolitis is difficult to differentiate from a viral exacerbation of asthma.
INVESTIGATIONS
Diagnosis is clinical.
Pneumonia
SIGNS / SYMPTOMS
Patients with community-acquired pneumonia typically present with symptoms and signs consistent with a lower respiratory tract infection (i.e., cough, dyspnoea, pleuritic chest pain, mucopurulent sputum, myalgia, fever) and no other explanation for the illness (e.g., sinusitis or asthma).
INVESTIGATIONS
Consolidation seen on chest x-ray.
Foreign body/obstruction
SIGNS / SYMPTOMS
May cause a localised wheeze, depending on the site of obstruction.
History may reveal a foreign body aspiration.
No significant improvement with bronchodilators.
INVESTIGATIONS
If the foreign body is radio-opaque, it may appear on a plain x-ray. Otherwise, a CT scan of the chest may suggest an endoluminal obstruction.
Fibreoptic bronchoscopy is the definitive test for diagnosis and treatment of a foreign body in the airway.
Vocal cord dysfunction
SIGNS / SYMPTOMS
Difficult to diagnose.
May occur independently from or concomitantly with asthma.
More common in young females.
Wheezing is often more prominent over the neck.
Symptoms may be precipitated by stress and patients may feel worse with bronchodilators as they could heighten anxiety.
Frequently inspiratory wheezing.
INVESTIGATIONS
A video laryngostroboscopic examination may show paradoxical vocal cord movement.
The classically observed pattern consists of adduction of the anterior two-thirds of the vocal cords with a posterior diamond-shaped chink. This occurs during inspiration but can be present during the entire respiratory cycle and can also be observed on the flow-volume loop as flattening of the inspiratory limb.
Heart failure
SIGNS / SYMPTOMS
History of left ventricular dysfunction with signs and symptoms of heart failure including crackles and rales on auscultation of the lungs and peripheral oedema.
INVESTIGATIONS
Presence of pulmonary oedema on chest radiographs should guide the clinician to a cardiac cause of symptoms.
Brain natriuretic peptide (BNP) may help to exclude cardiac cause if <100 nanograms/L (100 picograms/mL).[56]
Anaphylaxis
SIGNS / SYMPTOMS
More stridor than wheezing.
A history of an environmental exposure to a possible stimulus for anaphylaxis is essential.
INVESTIGATIONS
No differentiating tests.
Emphysema/COPD
SIGNS / SYMPTOMS
History of smoking that usually exceeds 20 pack-years.
COPD exacerbations and asthma exacerbations are clinically similar, with cough, shortness of breath, and wheezing the typical symptoms.
Patients with asthma are more likely to have episodic chest symptoms, night-time chest symptoms, and chest symptoms after exposure to allergic triggers.
Patients with COPD are more likely to have a daily morning cough that produces mucus, and persistent chest symptoms throughout the day.
INVESTIGATIONS
Patients with asthma will present with evidence of bronchial hyperreactivity and reversibility on pulmonary function tests more frequently than patients with COPD.
Carcinoid syndrome
SIGNS / SYMPTOMS
May have associated flushing, diarrhoea, or right-sided heart failure.
INVESTIGATIONS
Patients have significantly raised serum levels of serotonin or its metabolites, of which the most important is 5-hydroxyindoleacetic acid.
Pulmonary embolism
SIGNS / SYMPTOMS
Wheezing is unusual with pulmonary emboli but may occur with several small emboli.
Chest pain would be a differentiating feature.
History of risk factors for PE, including immobilisation, previous deep vein thrombosis (DVT)/PE, or cancer, in a patient with a sudden onset of dyspnoea should prompt additional testing for PE.
INVESTIGATIONS
A low-probability Wells score along with a negative D-dimer assay may rule out this diagnosis.
If clinical suspicion warrants, a CT pulmonary angiogram study or ventilation-perfusion (V/Q) scan can be performed.[57]
Allergic bronchopulmonary aspergillosis (ABPA)
SIGNS / SYMPTOMS
Occurs in 1% to 2% of asthma patients.
ABPA is a hypersensitivity reaction in patients with asthma or cystic fibrosis that may cause bronchial obstruction, mucus production, and wheezing.
Differential symptoms include fever, haemoptysis, and expectoration of brown mucus plugs.
INVESTIGATIONS
Chest radiograph may show pulmonary infiltrates or evidence of bronchiectasis.
Skin test reactivity or serum antibodies to Aspergillus are present.
Serum IgE is typically >1000 nanograms/mL and there is generally a peripheral blood eosinophilia of >500/mm3.[58]
Pneumothorax
SIGNS / SYMPTOMS
Can present with symptoms similar to an asthma exacerbation.
Shortness of breath and chest tightness are common symptoms of pneumothoraces.
INVESTIGATIONS
If clinical suspicion warrants, a chest radiograph can be performed to assess for a pneumothorax.
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